U.S. Pat. No. 3,432,194, including the prior art depicted and described in that patent, is illustrative of the type of coupling mechanism that has been used in the past to interconnect a handpiece motor section with any of a variety of straight or angular handpiece attachment sections. The coupling takes the form of a slip joint with one of the sections, usually the motor section, having a cylindrical sleeve adapted to be received within a socket in the other (handpiece) section. An external or internal latch connects the two parts to prevent axial separation without preventing relative rotation. In general, such a latch mechanism has a substantial axial length and the push button or other means for actuating the latch projects laterally from the outer surface of the handpiece section in which it is provided. The lateral projection of the button from the assembly is undesirable because it tends to increase the risk of inadvertent release of the latch. Although that risk may be reduced somewhat by decreasing the size of the button and the extent of lateral projection thereof, such modifications increase the difficulty of intentionally manipulating the latch when disengagement of the parts is desired. See also U.S. Pat. No. 3,604,735.
Other types of latching mechanisms have been devised, some of which include rings that do not project significantly beyond the outer surface of the handpiece and motor sections, the latches being actuated either by rotation of the rings or by axial displacement of such rings. (For an example of the latter, see U.S. Pat. No. 3,665,606). Where the mode of operation requires axial displacement of a latch ring, an undesirable axial spacing is commonly provided to accommodate such movement. In the case of a rotatable latch ring, a user may find manipulation difficult since two hands may be required to turn the ring relative to the motor section and then one of the hands must be shifted to urge the two sections axially apart.
The present invention lies in providing an assembly equipped with a latch mechanism which overcomes such defects and disadvantages of prior constructions. The latch mechanism, although capable of being released by the application of force over a substantial semi-circumferential area, is not likely to be inadvertently actuated because when the sections are latched together the latching element, in the form of a latching ring, has its outer surface flush with the outer surfaces of the handpiece and motor sections.
The latch mechanism of this invention is highly reliable in operation, providing relatively large latching surfaces which are less likely to wear, and become insecure by reason of such wear, than prior latch mechanisms. In addition, the latch ring or tube allows the flow of air therethrough for the purpose of cooling the bearings of the motor section and the handpiece attachment section.
Briefly, the assembly takes the form of a motor section and a handpiece section, each having a power-transmitting shaft or spindle axially disposed therein. When assembled, the sections are arranged in longitudinal alignment with the respective power-transmitting shafts thereof in operative engagement with each other. The latch ring or tube is carried by one of the sections, preferably the motor section, and is disposed between the two sections with its outer surface normally in flush relation with the outer surfaces of the adjoining sections. The ring is mounted to permit limited transverse movement thereof into an unlatching position, in which position an arcuate rib or projection formed within the ring is disengaged from a neck portion of the handpiece section to permit axial separation of the parts. In the absence of the application of force displacing the ring laterally into its unlatching position, a spring maintains the ring in latching condition. The ring has substantial axial length and, since it may be moved into its unlatching position by finger contact over an arc of its surface of approximately 180.degree., it provides a large contact area for finger engagement and operation. However, because its outer surface is normally flush with the casings of the handpiece and motor sections, the possibilities of snagging or otherwise interfering with manipulation of the handpiece, or of inadvertent release of the latch, are virtually eliminated.
Other features, objects, and advantages of the invention will become apparent from the specification and drawings.